The present invention relates to a method and device for controlling the tracking and, more particularly, to an improvement in a VTR or another type of magnetic tape recording/reproducing apparatus wherein tracking of a magnetic head on a track is properly performed in a playback mode in accordance with four pilot signals which have different frequencies and which are recorded, together with information signals, on a tape.
A conventional tracking control system for a magnetic tape recording/reproducing apparatus, especially a VTR, is described under the title "Method of controlling the position of a write or read head and a device for carrying out the method" in U.S. Pat. No. 4,297,733. According to the principle of this method, four tracking signals (pilot signals) having different frequencies are recorded, together with information signals, on sequential tracks in the recording mode. In the playback mode, the pilot signals are used to obtain tracking control signals.
According to the method described above, four pilot signals are provided having four frequencies f1, f2, f3 and f4 which satisfy the following conditions: .vertline.f1-f2.vertline.: .vertline.f2-f3.vertline.: .vertline.f3-f4.vertline.=1:3:1 or 3:1:3. These pilot signals are sequentially recorded on the tracks of a video tape as a record carrier in a cyclic sequence of f1, f2, f3, f4, f1, . . . In the playback mode, four reference signals having frequencies which satisfy the same conditions are provided in the same cyclic sequence as the pilot signals. Two difference frequency signal components are obtained from differences detected between a pilot signal component of an immediately preceding track (adjacent track) to a given reproduced track and a corresponding reference signal and between a pilot signal component of an immediately following track to the given reproduced track and a corresponding reference signal. For example, when the track recorded with a pilot signal of the frequency f2 is subjected to reproduction by the magnetic head, the pilot signals recorded on the right and left adjacent tracks, respectively, have the frequencies f1 and f3, and the corresponding reference signal has the frequency f2. Therefore, the frequencies of the two difference frequency signal components described above are given to be .vertline.f1-f2.vertline. and .vertline.f2-f3.vertline., respectively. Similarly, when the recording tracks having the pilot signals of the frequencies f3, f4 and f1 are played back, difference frequency signal components .vertline.f2-f3.vertline. and .vertline.f3-f4.vertline., .vertline.f3-f4.vertline. and .vertline. f4-f1.vertline., and .vertline.f4-f1.vertline. and .vertline.f1-f2.vertline. are obtained, respectively. Now assume that .vertline.f1-f2.vertline.=.vertline.f3-f4.vertline.=M and .vertline.f2-f3.vertline.=.vertline.f4-f1.vertline.=3M. The difference frequency signal components of the frequencies M and 3M are normally obtained when any track is set in the playback mode. These signals are detected from the reproduced signal, and the difference between the levels of these difference frequency signal components is detected so as to obtain a tracking control signal. Tracking control is then performed to compensate for the tracking control signal by means of a tracking servo circuit e.g. those may be zero. Thus, the head can be properly traced on the track in the playback mode.
According to this system, however, a ratio of a difference frequency signal corresponding to the difference between the reference signal and the pilot signal component which is detected from the right adjacent track of the reproduced track to the difference frequency signal corresponding to the difference between the reference signal and the pilot signal component which is detected from the left adjacent track thereof not constant but changes to be 1:3 and 3:1 in every other track. For this reason, when there is a difference between difference frequency signal components of the frequencies M and 3M, the resultant level difference signal is inverted in every other track even if a tracking error occurs in the same direction. Therefore, the inverted and noninverted difference signals must be switched in every other track in order to be extracted as tracking control signals. Thus, tracking noise is mixed in the tracking control signals, and tracking control becomes unstable. In addition, a polarity inverter, a control signal switching circuit and control circuits thereof are required, resulting in a complex circuit arrangement of high cost.
Furthermore, since the difference level signals must be inverted in every other track to obtain the tracking control signal, tracking position adjustment cannot be performed in principle. It is a problem take place depended on the head size and the head mounting position varies in each apparatuses by mass production. In this case, also correction must be performed to achieve proper tracking position adjustment.